The present invention relates to a device for performing jumps by successive leaps.
The type of device aimed at by the invention has, to a great extent, already been described in numerous publications, such as U.S. Pat. No. 4,390,178.
This patent describes a machine essentially comprising a tube inside which there slides an impact shaft, the deployment of which towards the ground is effected by means of a compression spring. The improvement made to this machine resides in the fact that the handlebar with grips and the footrest struts, which are fixed to the upper and lower ends of the tube respectively by means of a pin, are capable of pivoting about the axis of the tube and are interconnected via rigid metal rods. A configuration of this kind makes it possible to keep the handlebars and the struts in the almost horizontal position, whatever the inclination imparted to the impact shaft.
In this way, the user has better control of his machine on uneven ground. However, the inexperienced user cannot familiarise himself with a machine of this kind in complete safety.
The object of the invention is to remedy this drawback and to propose a jumping machine of the above mentioned type which enables an inexperienced user to familiarise himself with the said machine in complete safety.
Another objective of the invention is to provide a jumping machine which can be used in extreme conditions such as those of a sporting competition.
To that end, the subject of the invention is a device for performing jumps by successive leaps which comprises:
a tubular body which is provided at one of its ends, which is referred to as the xe2x80x9clowerxe2x80x9d end, with footrest struts,
a handlebar equipped with grips which is integral with the other end, which is referred to as the xe2x80x9cupperxe2x80x9d end, of the body,
an impact shaft which is adapted to slide inside the body and at least part of which is capable of being deployed in the extension of the lower end of the body, and means for returning the shaft elastically to an extreme deployed position.
According to the invention, the device is characterized by the fact that it comprises means for braking the impact shaft in relation to the body and means, which are disposed on the handlebar, for manually controlling the said braking means.
An inexperienced user can thus master the jumping device more easily with the aid of the braking means according to the invention, and therefore perform the initial jumps in complete safety.
Moreover, the device according to the invention can be used in extreme conditions, since the braking means are capable of instantaneously stopping the sliding of the impact shaft in relation to the body.
The footrest struts are preferably produced in a single, machined piece provided with an axial passage which is adapted to receive the impact shaft by sliding, the said machined piece being screwed to the lower end of the tubular body.
The handlebar is advantageously connected to the upper end of the body via a stem.
According to a preferred characteristic of the invention, the elastic returning means comprise a helicoidal spring.
The braking means advantageously comprise at least one friction surface which is adapted to rest radially against the shaft.
According to a preferred variant of the invention, the shaft is hollow and the friction surface rubs on the inside of the said shaft.
According to this variant, the friction surface is advantageously a cylindrical ring made of elastomer.
According to this variant again, the braking means comprise a bush which is adapted to deform the cylindrical ring radially.
According to the invention, the bush advantageously has, in its lower part, feet which each have an inclined face and are disposed in a concentric manner and around which the cylindrical ring is force-fitted. A needle having a conical head is preferably inserted between the feet, thereby coming into contact with each inclined face, the manual control means being adapted to displace the said needle axially with a view to causing the said feet to move apart radially.
Preferably again, the device comprises means for returning the needle elastically.
According to a preferred mode of embodiment of the invention, the device comprises a sleeve which is screwed to the upper end of the tubular body and extends longitudinally inside the latter in such a way as to accommodate the cables fixed to the braking means.
According to this mode of embodiment, the braking means are preferably fixed to the lower end of the sleeve.
The device according to the invention advantageously comprises a ball-socket which is adapted to guide the shaft along the axis of the body when it slides inside the